Demountable screen grid tube



Feb. 12, 1935.v A GEBHARD 1,990,482

DEMOUNTABLE SCREEN GRID TUBE File April 17, 1935 2 Sheets-She et 1 IN V EN TOR.

QOg VZ/D 9L gegfzamb Patented Feb. 12, 1935 ,tarsr (Granted under the act ofMarcli.3, "18'83, as

amended April 30, 1928; 370 0. G; 757) My invention relates broadly to high power screen grid electron tubes and more particularly to a demountable screen grid tube construction.

construction of demountable screen grid tube having means for substantially shielding the control grid while permitting disassembly of the tube when it becomes necessary to renew the filament electrode therein.

Still another object of my invention is to provide a construction of screen grid tube-for high power operation in which economy in the operating expense and replacement of the tube may be eiiected by providing such an arrangement of the tube elements as will permit disassembly of the tube for renewal of desired parts and reassembly and re-evacuation thereof for continued operation without replacement of the entire tube.

Other and further objects of my invention reside in the construction of a high power screen grid tube as set forth more fully in the specification hereinafter following by reference to the accompanying drawings, in which:

Figure l is a side elevation of-a tube constructed in accordance with my invention; Fig. 2 is a top plan view thereof; Fig. 3 is a bottom plan view thereof; Fig. 4 is a central vertical longi- 35 tudinal sectional view thereof taken on line 4-4 of Fig. 2, the chucks for holding the filament in place being shown in side elevation; Fig. 5 is a central vertical longitudinal sectional view on an enlarged scale taken substantially on line 5- 5 40 of Fig. '7, the tube being broken at the center and the parts greatly foreshortened; Fig. 6 is a sectional View or" the lower portion of the tube taken substantially on line 6-6 of Fig. 7 and showing more particularly the mounting of the 45 lower chuck and the adjacent portions of the grid and screen structure; and Fig. '7 is a horizontal sectional view taken on line '77 of Fig. 5.

The tube structure of my invention is extremely simple and does not require a breakable envelope of glass or quartz. The anode of the tube constitutes the main closure member and provides in association with removable end mem bers, a closed chamber which may be evacuated to the desired degree for operation of the tube. A- renewable filament structure is employed in the tube similar to the structure described more fully in my copendingapplication Serial No; 660,707, filed March 14, 1933.; A control grid insulatingly supported within the chamber "and surrounding the control grid'and adjacent the 5 anode I- provide ascreen grid structure." The screen grid structure is insulatingly mounted with respect to the other elements of-- the tube and is provided with special means" for shielding thecontrol grid. I provide annular shields shbported by the screen grid at opposite ends of the tub'e' which serve to edectively shieldthe tube. The-- electrodcs are so constructed that upon"disas'--- sembly of the tube to permit renewal of the filai ment or other elements, the replacement of the desired elements may be effected rapidly and the tube reassembled and re-evacuatedforcontinued operation. 1

Referring to the drawings in more det'a'il, the filament is shown at 1 heldby screw chucks 2- and 3. Chuck 2 is mounted" in end-plate 4'.- Chuck 3 is mounted in any suitable manner such as by brazingsoldering or welding to a resilient disc 5-which compensates for the' expansion of the filament and holdsit taut under variations in temperature. Disc 5 is mounted upon end plate 6 by means'ofscrews 5a andan nular member 50 as shown.- Disc 5 in this c'aseis flat instead of corrugated.- I A-fiatspring 51), se

cured in position by sc'rews5c. provides additional tension onthe chuck for maintaining the files--- ment taut under conditions oi expansion and contraction due to temperature changes. The control grid is shown generally ati 'l' and the screen grid generally at 3. The anode is shown at 9 with a'cylindrical member 10 surroundingit to provide a jacket 1 1' in which" cooling liquidis circulated. The cooling liquid enters at 1'2: and- Band discharges at'14 The anode -is' 'sup portedby cylindrical insulatingmeinbers '15 and 16 and'clamped with them' between the end plates 4 and 6 by means of insulating'rods; 1 7-" tightened by screws 18. Gaskets 1'9, 20', '21 and 22 are provided to make the several joints air tight. A connection to the exhaust' pump is shown at 23. The filament terrrlinals ZQa-hd are provided on end plates 4 and 6'- respectively as shown in Fig. 4. The control grid terminal 'is shown at 26 and the screen grid tnaiaaliaezv. Theterminal for the anode 9 is indicated at- 2 8 on the exterior of the'anode. The control grid 7"cons'ists of verticalrods-29 fastened to end rings 30 and 31' in any suitable": manner such asby welding, brazingor soldering. On the vertical rods 29*there "is supported spiral wound wire 32, constituting the control grid. The lower ring 31 has projections which serve to support the structure through insulator 33 and the grid terminal 26. The grid terminal consists of a metallic member 34 having a shoulder 35 which, in association with the insulating members 36 and 37, gaskets 33 and 39, serve to seal the terminal against leakage of air; nuts 40 and 41; and a washer 42 completing this assembly, as shown. The projection 43 from the end of ring 31 is clamped between nut 40 and shoulder 35 for establishing a good electrical connection to the control grid. The screen grid 8 is arranged to screen the control grid '1 from the anode 9 as completely as possible and thus reduce the capacity between these electrodes to a It extends to both ends of the tube and is brought to close proximity with the end plates 4 and 6. The screen grid 8 consists of vertical rods 44 fastened to end rings 45 and 46 supporting a wire mesh 47. The lower ring 45 has an integral flange 48 thereon which extends over the control grid terminal 34 and support 33 and forms an electrostatic and electromagnetic shield. The screen grid structure is also supported through the flange 48 as shown in. Fig. 6, by means of insulating pillar 49 and screw 50 on the one side and insulated terminal 2'? on the other side. A link 51, secured by the nut of the terminal 2'7, is tapped to receive screw 52 which passes through flange 48 and thus fastens it to the terminal 27. The flange 48 is cup shaped and is turned. downwardly in a skirt 48a to such a distance as will prevent undesired coupling of stray (magnetic and electrostatic lines of force with the tube elements. The shielding is made more perfect by the addition of a cap. 53 at the opposite end of the screen grid. Cap 53 has a laterallyextending portion for reducing'thecapacity betweenthe control grid 7 and anode 9 to a minimum. The cap 53'is arranged to be easily removed from ring 46 so that thetube may be readily assembled and disassembled with the demounting process. The cap 53 makes a tight, push fit over ring 46 and thus insures good electrical connection with screen grid 8. The shields in the opposite ends of the tube difler in construction for the reason that these shields have difierent functions to perform. Shield 53 is in, the form of a laterally extending flange as there are no terminals adjacent the flange. On the other hand, shield 48 must be shaped into the form of a cylinder or cup shaped member in order that the terminals 26 and 27 may be covered by the shield. In the claims herein I have pointed out particularly the construction of these shields in general terms and I desire that it be understood that modifications in the structure may be made without departing from the spirit of my invention. 7

The ends of cap 53, flange 48 of ring 45, and ends of anode 9 are rounded off so as to increase breakdown voltage. The rounded edges of the anode 9 are shown at 54 and 5.5. Thistype of construction affords much bettershielding of the control grid 7 by the screen grid 8 than is now obtained in air cooled tubes. This is due tothe eflicient disposition of the conducting and insulating parts of the tube. The use of metal end platesadjacent to the spread ends of the screen grid 8 assists considerably in effecting desired shielding. The insulating parts 15 and 16 supporting the anode 9 are so disposed that they are I located in an electric held of minimum intensity. losses in these parts aremaintained at a minimum. The temperature of the parts is kept low, which is essential to prevent air leaks in the demountable tube.

I have described my invention in one of its preferred embodiments but I desire that it be understood that I have in mind other structures of shield grid tubes and methods of assembly for the demountableparts thereof and I intend no limitations upon my invention other than are imposed by the scope of the appended claims.

The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalty thereon or therefor.

What I claim as new and desire to secure by Letters Patent of the United States as follows:

1. A demountable electron tube comprising a liquid cooledtubular anode, a pair of end closures secured upon said anode, liquid cooled means for detachably supporting a filament axially of said anode, a control grid carried by one of said end closures and concentrically disposed about said filament, a terminal for said control grid supported on the said last mentioned end closure,

and a screen grid electrode supported by the said last mentioned end closure and extend ng between said control grid and said anode. and a shield coextensive with said screen grid extending over said control grid terminal.

2. A demountable electron tube comprising a tubular anode, closure members for opposite ends of said tubular anode, a filament detachably mounted between said closure members axially of said tubular anode, a cylindrical control grid supported by one of said closure members and concentrically disposed about said filament, a cylindrical screen grid supported by one of said closure members concentrically between said control grid and said anode, and laterally extending shields connected with opposite ends of said screen grid one of said shields being demountable with respect to said screen grid.

3. A demountable electron tube comprising a tubular metallic anode, a closure for each end of said anode for forming a closed chamber Within said anode, a filament extending axially of said chamber, expansible and contractible chucks carried by each of said closures for removably mountported at one end from one ofsaid closures, and

flanges constituting shields extending from each end of said screen grid.

4. A demountable electron tube comprising a tubular metallic anode, a closure for each end of said anode for forming a closed chamber within said anode, a filament extending axially of said chamber, expansible and contractible chucks carried by each oi said closures for removably mounting said filament in said tube, tension means associated with one of said chucks, a cylindrical control grid disposed concentrically about said filament and supported at one end by one of said closures, a screen grid concentrically disposed between said control grid and said anode and supported at one end from one of said 010- sures, and laterally extending plates carried by each end of said screen grid and projecting totubular metallieanode, a closure foreach end of said anode for forming a closed chamber within said anode, a filament extending axially of said chamber, expansible and contractible chucks carried by each of said closures for removably mounting said filament in said tube, a cylindrical control grid disposed concentrically about said filament and supported at one end by one-of said closures, a screen grid concentrically disposedbetween said control grid and said anode and supported at one end from one of said closures, and laterally extending flanges carried by said screen grid and projecting toward said anode.

6. A demountable electron tube comprising a tubular anode constituting an envelope for the electron tube, a closure insulatingly secured to each end of said anode, a filament extending axially through said anode, means for removably supporting said filament between said closures, a cylindrical structure concentrically disposed about said filament and insulatingly supported from one of said closures, a control grid terminal extending through the said last mentioned closure and insulated therefrom, a control grid carried by said cylindrical structure and connected with said control grid terminal, a second cylindrical structure concentrically disposed between said first mentioned cylindrical structure and said anode, a tubular member insulatingly supported by said last mentioned closure and connected to support said second cylindrical structure, and a screen grid carried by said second cylindrical structure.

7. A demountable electron tube comprising a tubular anode constituting an envelope for the electron tube, a closure insulatingly secured to each end of said anode, a filament extending axially through said anode, means for removably supporting said filament between said closures, a cylindrical structure concentrically disposed about said filament and insulatingly supported from one of said closures, a control grid terminal extending through the said last mentioned closure and insulated therefrom, a control grid carried by said cylindrical structure and connected with said control grid terminal, a second cylindrical structure concentrically disposed between said first mentioned cylindrical structure and said anode, a tubular member insulatingly supported by said last mentioned closure and connected to support said second cylindrical structure, said tubular member extending over said control grid terminal and electrically shielding said control grid terminal.

8. A demountable electron tube comprising a tubular anode constituting an envelope for the electron tube, a closure insulatingly secured to each end of said anode, a filament extending axially through said anode, means for removably supporting said filament between said closures, a cylindrical structure concentrically disposed about said filament and insulatingly supported from one of said closures, a control grid terminal extending through the said last mentioned closure and insulated therefrom, a control grid carried by said cylindrical structure and connected with said control grid terminal, a second cylindrical structure concentrically disposed between said first mentioned cylindrical structure, and said anode, a tubular member insulatingly supported by said last mentioned closure and connected to support said second cylindrical structure, said tubular member being enlarged in diameter at the extremity thereof and extending over and substantially enveloping said control grid terminal for electrically shielding the said terminal.

9. A demountable electrontube comprising .a cylindrical anode, cover members for opposite ends of said cylindrical anode, tension means fo'r maintaining said cover members in substantially airtight but electrically [insulated engagement with opposite ends of said cylindrical anode, filament engaging means supported by each of said cover members, a filament adapted to bare movably -mounted in said filament engaging means, a cylindrical frame concentrically disposed about said filament, means for insulatingly supporting said cylindrical frame from one of said cover members, a control grid terminal insulatingly mounted in the said last mentioned .cover member, a control grid carried by said cylindrical frame and electrically connected withthe said control grid terminal, a cylindrical member insulatingly mounted on said last mentioned cover member and having a diameter substantially equal to the diameter of said anode and substantially enveloping the supports for said cylindrical frame and said control grid terminal, said cylindrical member having a portion thereof reduced in diameter and extending toward said anode, and a second frame structure supported by the reduced portion of said tubular member extending intermediate said control grid and said anode, and a screen grid carried by said second frame structure.

10. A demountable high power electron tube comprising a cylindrical anode, insulated sleeves surrounding opposite ends of said cylindrical anode, metallic cover members extending laterally across the ends of said insulated sleeves, longitudinally extending rod members exterior to said cylindrical anode and extending through said cover members, said rod members constituting means for compressing said cover members, said sleeves and said anode in substantially airtight engagement, means supported by said cover members for removably mounting a filament axially of said anode, and a pair of removably mounted grid electrodes disposed intermediate the filament and said anode.

11. A demountable high power tube comprising a cylindrical anode, a cover member insulatingly engaged with each end of said cylindrical anode, a filament extending axially through said anode and removably mounted with respect to said cover members, a pair of coextensive grid electrodes removably supported in said tube between said filament and said anode, and shield members extending from opposite ends of one of saidgrid electrodes, one of said shield members being demountable with respect to said grid electrode.

12. A high power demountable tube comprising a tubular metallic anode forming a chamber for the tube, means for insulatingly closing opposite ends of the anode and effecting a substantially gastight seal therewith, a filament extending axially of said anode, means for removably supporting said filament with respect to said first mentioned means, a pair of cylindrical grid structures removably supported in said tube between said filament and said anode, and shields carried by one of said cylindrical grid structures extending beyond the conductive limits of the other of said cylindrical grid structure.

13. A high power demountable electron tube comprising a tubular anode, closure members insulatingly connected with opposite ends of said anode, tension means interconnecting said closure members for rendering the chamber within said anode substantially airtight, a filament extending axially of said chamber and rinovably' supported by said closure members, a control grid concentrically disposed about said filament and removably mounted within said chamber, a screen grid disposed between said control grid and said anode, and means for removably mounting said screen grid within said chamber, said screen grid havingextensions on each end thereof projecting beyond the'limits of said control grid.

14. A high power demou'ntable electron tube comprising a tubular anode, closure members insulatingly connected with opposite ends of said anode. tension means interconnecting said closure members for rendering the chamber within said anode substantially airtight, a filament extending axially of said chamber and removably supported by said closure members, a control grid concentrically disposed about said filament and removably mounted within said chamber, a screen grid disposed between said control grid and said anode, and means for removably mounting said screen grid within said chamber, a flange member connected with one endof said screen grid and projecting toward said anode and a cup shaped member connected with the other end of said screen grid and projecting in a plane normal to the axis of said anode throughout one portion of its length and in concentric alignment with the anode throughout another portion of its length.

LOUIS A. GEBHARD. 

